Apparatus for annealing continuous metal bands in a vacuum



Nov. 21, 1967 A. LICHTE 3,353,806

APPARATUS FOR ANNEALING CONTINUOUS METAL BANDS IN A VACUUM Filed March 11, 1963 fzuounua uv z rarlulllllll lwl 3,353,806 APPARATUS FOR ANNEALING CONTINUOUS METAL BANDS IN A VACUUM Albert Lichte, Wuppertal-Elberfeld, Germany, assignor to Schloemann Aktiengesellschaft, Dusseldorf, Germany Filed Mar. 11, 1963, Ser. No. 264,164

Claims priority, application Germany,

Mar. 30, 1962, Sch 31,223 3 Claims. (Cl. 266-3) The demand for the production of metals and metallic alloys with the smallest possible content of impurities has led, amongst other things, to the development and employment of annealing furnaces and annealing apparatus with a controlled annealing atmosphere. The so-called protective gas furnaces, in which the annealing process is carried out in an atmosphere of gas that is inert to the material being annealed, are known and widely used in this connection. Besides these protective-gas furnaces, however, vacuum furnaces and vacuum annealing appliances have also become known, in which the annealing of the materials to be treated is effected in a vacuum; for by annealing in a vacuum, metals and alloys, even in a solid condition, can be decisively influenced not only in their chemical and physical properties but also in their technological properties.

In the known vacuum annealing devices or vacuum annealing furnaces that have hitherto found entry into practice, it is a question-of so-called pot annealing plants or hood annealing plants. Steel bands or similar band-like or cord-like material is annealed in these plants in a coiled condition, that is, in an entire ring or bunch, in a discontinuous operation. Since, in the vacuum, the transmission of heat from the furnace walls to the material that is being annealed can only be effected by radiation, the outsides of the rings or bunches are exposed substantially more strongly to the annealing process than the interior parts. This gives rise to certain differences in quality, the coarsening of grain of the more strongly annealed parts of the material being particularly objectionable. A further disadvantage of the known pot or hood annealing plants is that these plants only work ecenomically with relatively small throughput quantities.

For large throughput quantities a continuous operation seems more economical. Only an experimental plant of such a nature has however become known up to the present. In this continuous or pusher-type vacuum furnace for the heat treatment of metal bands, the vacuum is maintained by special air sluices mounted at the entry and exit ends of the band. In the known experimental plant these sluices are constructed as pressurestage chambers. The slot-like inlet and outlet apertures for the band are here located in the free air space, so that air also flows into the plant along with the band, and has to be sucked out again. A pre-determination of the quantity of air flowing into the gap is very uncertain, since the quantity of air flowing in is already subjected, bytransient variations in the cross section of the band, to remarkably large fluctuations. It is therefore hardly possible to keep the vacuum always constant. Moreover the magnitude of the fluctuations increases very disadvantageously in larger plants.

The fluidtight packing of the band at the inlet and outlet slots is unsatisfactory, and furthermore, by the current of air flowing in, the band is excited to violent oscillations, which may even lead to the complete destruction of the band. This plant has therefore not provided the desired success, and has not found any entry into practice.

Now this invention is based on the problem of providing, for the continuous heat treatment of endless metal United States Patent bands, a continuous or pusher-type vacuum annealing means which obviates the disadvantages enumerated.

The invention relates to apparatus in which the annealing chamber is closed in an airtight manner by vessels containing liquid, and the annealing heat of the material to be annealed is produced by passing an electrical heating current through this material, the closure of the circuit being effected by liquid consisting of molten metal.

The invention consists in the feature that the apparatus consists of a plurality of vessels, arranged in two stages one above the other, which are connected with one another by vertically extending connecting tubes, and that the guiding means conveying the band to be treated through the apparatus, particularly rollers or the like, are journalled in the containers, the lower containers serving at the same time as liquid-containers, whilst the upper containers are constructed as vacuum vessels and are in communication with evacuating means, the closure of the electric circuit being established by two liquid contacts consisting of molten metal.

By this construction and arrangement of the apparatus, the vacuum chamber is kept exceedingly small in relation to the purpose for which it is used, in comparison with other plants, and the production of a reduced pressure, down to practically absolute vacuum, is possible, since according to the height of the vacuum a corresponding column of liquid sealing medium can ascend from -the liquid-containers into the connecting tubes, that is to say, into the vacuum chamber.

The apparatus itself may be of comparatively light weight, since the heat of the electrically heated metal band in the vacuum is transmitted to the connecting tubes only by radiation from the band, for which reason a fire proof lining of the apparatus is unnecessary.

A particularly advantageous form of construction of the invention consists in the provision of a plurality of containers, preferably three, for liquid, of which the two outer containers seal the vacuum chamber from the atmosphere, whilst the middle container subdivides the apparatus, and the vacuum chamber, into an annealing zone and a cooling zone. By this division of the apparatus into an annealing zone and a cooling zonethe advantage is obtained that the connecting tubes do not take up any heat in the cooling zone owing to the annealing operation itself, but need only remove radiation heat of the band, for which reason the cooling time is materially shortened. The whole of the heat treatment can therefore always be effected under controllable conditions.

It is furthermore advantageous that the entire apparatus consists of only three constructional members, which are all alike. The apparatus can therefore be expanded' and enlarged to any convenient extent. Since the treatment capacity depends upon the annealing time and cooling time required by the band, and therefore also upon the speed of travel of the band, the arrangement ofthe connecting tubes renders it possible, by merely lengthening the same, to increase the output considerably,'without alterations being necessary in the other constructional parts of the apparatus. Similarly the apparatus can be lengthened, in front or at the rear, that is to say, at the. inlet end or at the outlet end of the band, by putting on further constructional members at will; By this means also, further treatments, either before or after the actual annealing operation, can be carried out in a vacuum in one and the same apparatus. Complicated and expensive separately erected after-treatment plants can accordingly be dispensed with. By this means all the expenses of treatment prove more favourable, even if a comparison of the pure annealing costs shows higher values owing to the electrical healing.

Furthermore, these continuous annealing plants can dispense with the otherwise usual expensive looping pits r looping towers for storing the band, since by welding together the band ends for example, the passage of the band through the plant according to the invention may be interrupted without any disadvantageous influence; for the annealing temperature can be very easily and quickly regulated over large temperature ranges by controlling the direct electrical resistance heating of the band.

One form of construction of apparatus according to the invention is illustrated by way of example in the accompanying drawing.

The vacuum annealing apparatus according to this constructional example consists essentially of three liquid-containers 1, 2, 3, set up side by side in one plane, two vacuum vessels 4, arranged above them in a second plane, and four vertically extending connecting tubes 6, 7, 8, 9, by which the liquid-containers are connected with the vacuum vessels. In order to ensure a satisfactory coupling of the connecting tubes 6, 7, 8, 9, each of the liquid containers 1, 2, 3 is provided with two upwardly directed sockets or sleeves 1a, 1b, 2a, 2b, 3a, 3b, whilst the vacuum vessels 4, 5 each have two downwardly directed sockets or sleeves 4c, 4d and 5c, 5d. The first liquid-container 1 is connected by way of the socket 1b, the connecting tube 6 and the socket 40 with the vacuum vesel 4, whilst the same vacuum vessel 4 is in communication, by -way of the socket 4d, the connecting tube 7 and the socket 2a, with the second liquid-container 2. This second liquid-container 2 is then connected, by way of the socket 2b, the connecting tube 8 and the socket 5c, with the second vacuum vessel 5, from which the connection is passed on, by way of the socket 5d, the connecting tube 9 and the (socket 3a, to the liquid container 3. Thus a continuous communication is provided for the passage of the band, the socket 1a of the liquid-container 1 serving as an inlet into the apparatus, and the socket 3b of the liquidcontainer 3 serving as an outlet from the apparatus.

The connecting tubes '6, 7, 8 and 9, and the sockets 1a, 1b, 2a, 2b, 3a and 3b may be of any desired cross section, even square or rectangular. Since, upon the apparatus being evacuated, the tubes are exposed, owing to the internal vacuum, to heavy pressures, a round, or at least oval form of tube will be selected in most cases, on grounds of strength. For the actual guidance of the band, guide rollers 10 are provided, which are journalled within the liquid-containers 1, 2 and 3, and guide rollers 11 within the vacuum vessels 4 and 5. A band entry roller 12 and a band exit roller 13 are located on a level with one another outside the apparatus itself.

Since, during operation, the liquid-containers 1, 2 and '3 are filled with a metal melt serving as a contact liquid, or with other treatment liquids serving for the treatment of the band, the guide rollers 10, and also their bearings, must be made of high-grade heat-proof and corrosionproof steel. The upper guide rollers 11, journalled in the vacuum vessels 4 and 5, are provided with an asbestos or ceramic coating. The guide rollers 10 and 11, according to the temperatures of treatment, may also be provided with water cooling, the water being admitted into the containers or vessels in a vacuum-tight manner.

The liquid-containers 1 and 2 are filled with a molten metal, whilst a fused salt is introduced into the liquidcontainer 3. The molten metals in the liquid containers 1 and 2 serve as liquid contacts, for the purpose of transmitting to the band itself the heating current necessary for heating the band 15. As a source of current a transformer 14 is provided, the secondary winding of which is connected by each of its poles to one of the liquid-containers 1 and 2 by way of electrodes 21, in such a way that the molten baths themselves are traversed by the current. The fused salt in the 1iquid-container 3 serves for the aftertreatment of the annealed band 15.

With this arrangement the molten baths provided in the two outer liquid-containers 1 and 3, which are in communication with the atmosphere through open sockets 1a and 3b, constitute at the same time liquid seals and prevent the penetration of atmospheric air into the apparatus.

Since the metal band 15 to be treated, in its passage through the apparatus, is traversed by the heating current only on its way bet-ween the liquid-container 1 and the liquid-container 2, the apparatus, and therefore also the vacuum chamber, are subdivided, by the arrangement of three liquid-containers, into an annealing zone and a cooling zone. In order that no disturbances may occur in the operation of the apparatus owing to short-circuiting through the apparatus, the liquidc0ntainers 1, 2 and 3, together with all the connecting tubes 6, 7, 8, and 9, are insulated from the vacuum vessels 4 and 5. For the insulating of the liquid-containers 1, 2 and 3 there serve insulators 16, whilst the insulating of the connecting tubes 6, 7, 8 and 9 is effected by means of insulating rings 17.

The production of the vacuum is effected by means of separately installed vacuum-producers, not represented in the drawing, such for example as pumps, steam-jet means, condensers or the like. By way of pipe lines, also not shown, these vacuum-producers are connected with the vacuum vessels 4 and 5 through sockets 13. During operation, the melts in the liquid-containers 1, 2 and 3 are drawn up into the vacuum chamber, that is to say, into the connecting tubes 6, 7, 8 and 9, in dependence upon the vacuum, a different liquid level adjusting itself according to the specific gravity of the melts. Owing to the lower specific gravity of the fused salt in the liquidcontainer 3, the liquid level in the connecting tube 9 will come to stand higher than the liquid level of the molten metals in the connecting tube 6.

As a material for the metal melts, tin is preferably employed. Lead or similar metals may however also be used. Not only for the metal melts, but also for the fused salt melt serving as after-treatment, it is important that a material of low melting point but of high boiling point should be employed. The fused salt is preferably an alkaline melt, which re-dissolves any reaction product formed on the material treated.

In order to bring not only the metals but also the salt to the necessary melting temperature, particularly when taking the apparatus into operation, heating strips or like heating devices 19, adjustable by means of transformers, are mounted in the liquid-containers 1, 2 and 3. These heating devices 19 are independent of the heating circuit for heating the metal band 15.

Since not only the metal melts but also the fused salt must not evaporate during operation, and must therefore not reach their vaporisation temperatures, which are low in a vacuum, cooling coils 20 are also provided in the liquid-containers 1, 2 and 3 in order to obviate an inadmissible rise of temperature of the melts owing to the hot metal band 15.

The size of the liquid-containers 1, 2 and 3, the volume of the metal melt, and the size of the electrodes 21, must be so dimensioned that the heating current can be transmited to the metal band 15 without damaging the material that is being annealed by burning it. Here, of course, the resistance and the cross section of the particular band, and also the annealing length and the annealing temperature of the band, must be taken into consideration.

Deviations from the form of construction described here and diagrammatically illustrated in the drawing may be made without altering or going outside the ambit of the invention. Thus, for example, in order to increase the cooling of the material under treatment during its passage through the cooling zone, Water or air cooling may be provided on the connecting tubes 8 and 9, in order to remove, as rapidly as possible, the heat of radiation coming from the metal band 15. Instead of applying external cooling means to the connecting tubes, however, it is also possible to inject saturated steam into the apparatus for the purpose of enhancing the cooling action. This steam, which becomes further heated on contact with the material that is being annealed, and which accordingly removes heat from this annealing material, is then sucked out again by steam-ejectors, and deposited in an associated con-denser, the condensation therein having the effect of raising the vacuum.

The apparatus according to the invention may moreover at any time be lengthened as desired by fitting on additional liquid-containers and vacuum vessels. In this manner further treatments in a vacuum may be very simply carried out in conjunction with the annealing process. Moreover the connecting tubes 6, 7, 8 and 9 may be lengthened in any convenient manner, in order for instance to increase the length of the annealing tract or of the cooling tract. In doing this, the annealing or cooling tracts can be individually lengthened independently of one another, by lengthening only the corresponding connecting tubes. If the increase in the height of the cooling plant that would be involved by lengthening the connecting tubes is not practicable, on structural grounds for example, the annealing tract can be lengthened by leaving one liquid-container dry, so that the band to be treated traverses two loops before it dips into a melt again. The annealing apparatus must then of course be lengthened in the horizontal direction by adding further structural members, and the arranging of the liquid contacts must then be such that the metal melts are located for instance in the first and third liquidcontainers.

A further modification, as compared with the constructional example, may consist in the feature that the vacuum vessels 4 and represented in the drawing are united into one continuous vessel.

1 claim:

1. Vacuum annealing apparatus for the continuous through-pass thermal treatment of a metal band, comprising: at least three similar liquid-containers, at least two similar vacuum vessels arranged above the liquidcontainers, there always being one less vacuum vessel than liquid-container, vertically extending connecting tubes placing the interior of each vacuum vessel in communication with the interior of two adjacent liquid-containers, means for guiding the band to be annealed through the liquid-containers, the connecting tubes and the vacuum vessels, at least two of the liquid-containers containing a metallic melt, at least one of said containers containing a fused salt, means for passing an electric heating current through the metallic melt into the band to be annealed and any vacuum vessel which is in communication with any container containing a fused salt providing a cooling zone for said heated band.

2. Vacuum annealing apparatus as claimed in claim 1, further comprising, on each liquid-container and on each vacuum vessel, an inlet socket and an outlet socket, by which the connecting tubes are attached to the liquid containers and to the vacuum vessels, and through which the band to be annealed enters and leaves the liquidontainers and the vacuum vessels.

3. Vacuum annealing apparatus as claimed in claim 1, further comprising cooling coils and adjustable heating means located within the liquid-containers, to enable the temperature of the liquids contained therein to be maintained within predetermined limits.

References Cited UNITED STATES PATENTS 2,418,087 3/ 1947 Nachtman 2663 2,926,902 3/1960 Roth et al 2663 3,163,566 12/1964 Jenkins et a1. 2663 FOREIGN PATENTS 710,081 6/ 1954 Great Britain. 718,835 11/1954 Great Britain.

JOHN F. CAMPBELL, Primary Examiner.

M. L, FAIGUS, Assistant Examiner, 

1. VACUUM ANNEALING APPARATUS FOR THE CONTINUOUS THROUGH-PASS THERMAL TREATMENT OF A METAL BAND, COMPRISING: AT LEAST THREE SIMILAR LIQUID-CONTAINERS, AT LEAST TWO SIMILAR VACUUM VESSELS ARRANGED ABOVE THE LIQUIDCONTAINERS, THERE ALWAYS BEING ONE LESS VACUUM VESSEL THAN LIQUID-CONTAINER, VERTICALLY EXTENDING CONNECTING TUBES PLACING THE INTERIOR OF EACH VACUUM VESSEL IN COMMUNICATION WITH THE INTERIOR OF TWO ADJACENT LIQUID-COMTAINERS, MEANS FOR GUIDING THE BAND TO BE ANNEALED THROUGH THE LIQUID-CONTAINERS, THE CONNECTING TUBES AND THE VACUUM VESSELS, AT LEAST TWO OF THE LIQUID-CONTAINERS CONTAINING A METALLIC MELT, AT LEAST ONE OF SAID CONTAINERS CONTAINING A FUSED SALT, MEANS FOR PASSING AN ELECTRIC HEATING CURRENT THROUGH THE METALLIC MELT INTO THE BAND TO BE ANNEALED AND ANY VACUUM VESSEL WHICH IS IN COMMUNICATION WITH ANY CONTAINER CONTAINING A FUSED SALT PROVIDING A COOLING ZONE FOR SAID HEATED BAND. 